The present invention relates to a base station and a method for controlling radio resources allocation in a base station. In particular, the invention relates to the fields of radio access in cellular communications systems, radio resource allocation and adaptive radio transmission.
In recent years, rapid advances in integrate-circuits and digital signal processors in the growth of Moore's law have given radio systems much more powerful baseband processing capabilities than ever before, which allows state-of-the-art wideband cellular systems to be dynamically adjusted in the use of its radio symbols or even the waveform.
Filter-bank based multi-carrier (FBMC) transmission as described by P. Siohan, C. Siclet and N. Lacaille: “Analysis and design of OFDM/OQAM systems based on filterbank theory,” in IEEE Transactions on Signal Processing, vol. 50, no. 5, pp. 1170-1183, May 2002 and by F. Schaich: “Filterbank based multi carrier transmission (FBMC)—evolving OFDM: FBMC in the context of WiMAX” in 2010 European Wireless Conference (EW), 2010, pp. 1051-1058 is a multi-carrier transmission scheme that allows the cellular system to use arbitrary adjustable pulse shapes for transmission. Pulse shapes may be adapted to requirements from the regulatory spectral mask, the mobility conditions with respect to the robustness against high Doppler Effect and the desired degree of robustness, e.g. synchronization errors. A spectrally efficient FBMC system can be realized based on OQAM-OFDM signaling.
By selecting suitable pulse shapes, FBMC systems generate very low out-of-band leakage. Thereby, the guard-band between two non-orthogonal systems operating next to each other in the frequency band is significantly reduced. In contrast, only incremental advances were observed in the radio frequency frontends of cellular system in recent years in terms of improving the instruments' linearity and dynamic range. Consequently, the modulation order for radio symbols is practically limited due to implementation and cost factors.
In this context, one transmission mode called “Faster Than Nyquist” (FTN) as described by D. Dasalukunte, F. Rusek, and V. Owall: “Multicarrier Faster-Than-Nyquist Transceivers: Hardware Architecture and Performance Analysis,” in IEEE Transactions on Circuits and Systems I: Regular Papers, vol. 58, no. 4, pp. 827-838, April 2011 has been proposed by academia to achieve higher data rate for the transmission with limited modulation orders, so as to substantially improve the radio efficiency when channel conditions are extremely good, i.e., at high signal-to-noise ratio.
With allowing configuring the waveform, specifically the pulse shapes when using the FBMC technology, as well as the transmission modes, specifically the FTN, two new degrees of freedom are gained when allocating the radio resources in cellular systems. For today's radio systems, adaptive modulation and coding (AMC) schemes are used to adapt the transmission signaling to the specific link conditions. These allow an adaptation of the signaling per link in two dimensions: the modulation constellation and the code rate. Additionally, transmit power allocation schemes have been proposed and are in use today. For future systems, a significantly increased variation of service demands and a large variety of user terminal types are foreseen. Along with the diverse channel selective characteristics, i.e., channel conditions observed on each radio link, the problem space spanned for the radio resource allocation problem is considered to be significantly increased in its dimensions.
If common radio resource allocation strategies like AMC are applied for systems based on a fixed signaling scheme like OFDM, the following drawbacks are encountered. First, the system fails to take advantage of extremely good channel conditions and only leads to moderate data rate transmission. Further, the system neglects to take a group of high mobility users into account. Due to the high Doppler Effect, the traditional OFDM systems suffer from high frequency offset that distorts the performance severely. OFDM based systems have strong requirements on frequency and time domain synchronization. Poorly synchronized systems, e.g., low-power low-cost sensor devices suffer from severe performance degradation. The system has to fulfill strict out-of-band leakage requirement by the regulator when accessing some specific spectrum bands that are shared with other systems. The edge-band usage of conventional OFDM signal causes a substantial waste of large guard-bands, in particular if only a narrow spectrum band is available.
The prior art of transmission scheme that is frequently applied on nowadays LTE and WiMax systems is called “Adaptive Modulation and Coding” (AMC) according to TSGR1#17 (00)1395, “Adaptive Modulation and Coding (AMC),” Stockholm, Sweden, 2000. It is usually combined with OFDM or spread coding, i.e., CDMA schemes to adaptively select a suitable set of transmission parameters, namely modulation and coding scheme (MCS), i.e. modulation/constellation order and coding rate. For the application on LTE systems, by dynamically receiving the feedback of Channel Quality Indication, together with the QoS requirements from higher layers, i.e. data rate, packet loss rate, etc., the LTE MAC scheduler decides the most suitable MCS either user-wise or physical-resource-block wise. The parameters of prior art systems, such as the length of the cyclic prefix and the subcarrier spacing are only long-term system-specific parameters that cannot be dynamically adjusted.